A while back I read an analyis that had the boil off rate to determine the Delta T between the liquid and metal. It was not very hig, the metal temp was less than 220F at the interface, below caramelization temps.

Thanks for the info, Jeff. I can't imagine why it would be any different.

I will add this one data point to the discussion, though I imagine there were mitigating circumstances:

I accidentally pinned a cotton hop bag to the bottom of my kettle with the IC for the last 15 minutes of the boil. When I discovered this, after draining the wort into fermenters, the hop bag was black and charred through (there was actually a hole burned through the hop bag). It had carbonized while under 10 gallons of boiling wort. I"m pretty sure spontaneous combustion of cotton requires temps in excess of 400*. So at least locally, sandwiched between a stainless pot bottom and a copper coil with a 200k BTU (or whatever a bayou classic is) propane burner, you can achieve temps well above 212.

With no liquid circulation, I agree.

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Jeff RankertAnn Arbor Brewers Guild, AHA Member, BJCP CertifiedHome-brewing, not just a hobby, it is a lifestyle!

A while back I read an analyis that had the boil off rate to determine the Delta T between the liquid and metal. It was not very hig, the metal temp was less than 220F at the interface, below caramelization temps.

Thanks for the info, Jeff. I can't imagine why it would be any different.

I will add this one data point to the discussion, though I imagine there were mitigating circumstances:

I accidentally pinned a cotton hop bag to the bottom of my kettle with the IC for the last 15 minutes of the boil. When I discovered this, after draining the wort into fermenters, the hop bag was black and charred through (there was actually a hole burned through the hop bag). It had carbonized while under 10 gallons of boiling wort. I"m pretty sure spontaneous combustion of cotton requires temps in excess of 400*. So at least locally, sandwiched between a stainless pot bottom and a copper coil with a 200k BTU (or whatever a bayou classic is) propane burner, you can achieve temps well above 212.

Sure, the bottom of your kettle can get hotter than 212. Liquid won't, though. It will boil harder, but not hotter.

Sure, the bottom of your kettle can get hotter than 212. Liquid won't, though. It will boil harder, but not hotter.

If it were that simple, then you'd never have to worry about scorching LME.

A few points to further complicate the conversation without offering anything more than mere conjecture.

Yes, liquid water will remain at its boiling point and no higher during the boil. Anything dissolved in said water would be at the same temperature as well. The thing is as soon as it becomes steam all bets are off and there is no maximum temperature. In addition not everything in the wort is dissolved. Larger particles are suspended and therefore could come in contact with said superheated steam directly.

Now, since the vast majority of the liquid (which posseses a rather large thermal mass) is set in stone in the ballpark of 212F, this superheated steam would rapidly come into equilibrium with the rest of the liquid as it rises through it.

Basically here's my opinion. There is a non-negligible chance that proteins suspended in wort could experience temperatures right at the hottest parts of the kettle to experience some Maillard reactions. But I have a tough time believing it would be a significant amount unless you're talking about a large, commercial-scale, direct-fire burner. Please note that this is a complete WAG, and I am not a physicist - I merely play one on the message boards.

You're not getting superheated steam in the boil. Solids like LME will stick to the bottom and scortch, but in an all grain boil I would think this is negligable, since I've never had any residue stuck to my kettle.

any physics type guys know what the pressure would be at the bottom of 200 gallons of wort? and would this actually make a difference in the boiling point of water at the bottom of a very large kettle than at the top?

If you estimate 3psi increase...then you are boiling at about 104...106 degC... so about 222degF. However...also keep in mind that the wort is constantly turning over, so it is not like there is wort constantly heated at 222 during the entire boil...just for a short period....and then it rises to the top,

Regardless of what the literature says about the conditions needed for the reactions of caramelization and'or Maillard, we know from direct observation that some darkening of wort does occur on boiling. So its safe to say that one or the other or both of these does happen to a limited extent. I don't think its a significant contributor to flavor though, I think thats mostly from kilning malt. And I guess to my original question, boiling probably doesn't drive off crosslinked amino acid-sugar complexes.

I do believe that reactions happen that add flavor (and color, of course). It's not caramelization though, at least to an extent that you can taste. Boil down some first wort runnings to the point that enough water evaporates, like candy making, and you'll taste caramelization.

Just some comments on superheated steam. There are two (or three) boiling regimes. The first is where bubbles of steam form on the bottom of the pot and then rise through the liquid. If you boil harder, the bottom of the pot can be covered by a layer of superheated steam which insulates the bottom of the pot from the water. I don't think that anyone intentionally boils their wort this way because it would cause a massive boilover once the layer of superheated steam breaks off from the bottom.

I don't recall seeing any comments about increased temperatures at the bottom of the kettle because of increased sugar concentrations at the bottom of the kettle due to the sugars in the wort that become steam being ejected into the surrounding solution. I would expect that this would happen causing the boiling point to rise some but I don't have much insight without busting out some chemistry textbooks.

The fact that beer darkens upon boiling is due to Maillard reactions. Caramelization occurs at higher temps and is similar to the Maillard reaction. Here's the three steps as laid out by a scientific study.

1. The first stage involves the sugar-amine condensation and the Amadorirearrangement. The reaction steps have been well-defined and no browning occursat this stage.2. The second stage involves sugar dehydration and fragmentation, and amino aciddegradation via the Strecker reaction especially at high temperatures as used incandy manufacture. At the end of stage two there is a beginning of flavor formation -depending on which flavor is studied.3. Formation of heterocyclic nitrogen compounds. Browning occurs at this stage.

The fact that beer darkens upon boiling is due to Maillard reactions. Caramelization occurs at higher temps and is similar to the Maillard reaction. Here's the three steps as laid out by a scientific study.

1. The first stage involves the sugar-amine condensation and the Amadorirearrangement. The reaction steps have been well-defined and no browning occursat this stage.2. The second stage involves sugar dehydration and fragmentation, and amino aciddegradation via the Strecker reaction especially at high temperatures as used incandy manufacture. At the end of stage two there is a beginning of flavor formation -depending on which flavor is studied.3. Formation of heterocyclic nitrogen compounds. Browning occurs at this stage.

That's a little too dense for me, but I thought the maillard reactions were occuring during kilning and only to a limited degree in the kettle. I do not dispute the darkening of wort over a vigorous boil, however.